The present technology relates generally to a sealing structure between a rotating component and a stationary component and, more particularly, to a compliant plate seal arrangement that overcomes dynamic instabilities.
Dynamic sealing between a rotor (e.g., rotating shaft) and a stator (e.g., static shell or casing) is an important concern in turbomachinery. Several methods of sealing such as labyrinth seal, brush seal and compliant plate seal have been used. A non-contact labyrinth seal may be used. At certain sealing locations with large rotor transients, labyrinth seals are assembled with relatively large radial clearance to avoid contact of the labyrinth teeth with the rotor and further opening of the radial clearance. Known labyrinth seals are based on rigid members and have a high differential pressure capability, but their leakage is relatively large due to the large radial clearance.
Brush seals consist of tightly packed, cylindrical bristles that are arranged in a staggered arrangement to reduce leakage. The bristles have a low radial stiffness that allows them to move in the event of a rotor excursion while maintaining a tight effective clearance during steady state operation. Brush seals also have a low stiffness in the axial direction because of the generally cylindrical geometry of the bristles. When subject to a high differential pressure across the seal, the bristles deflect in the axial direction towards the low-pressure side. This opens up the radial clearance and leads to high leakage across the brush seal. Brush seals therefore are generally effective only up to a limited differential pressure across the seal. Moreover, the bristles of a brush seal rub against the rotor surface leading to abrasion wear and heating of the rotor and the bristles. As a result, the bristles have to be made out of expensive material with wear resistance at elevated temperatures. The abrasion wear leads to opening of the clearances and requires frequent replacement of the expensive brush seals. Rotor heating may also lead to rotor-dynamic instability.
Some known compliant plate seals have been used as an alternative to brush seals. Conventional compliant plate seals include compliant plates attached to a stator in a circumferential fashion around a rotor. Compliant plates have increased differential pressure capability due to larger axial stiffness to radial stiffness ratio of the compliant plates compared to bristles in brush seals. The differential pressure capability of conventional compliant plates is limited due to uncontrollable hydrostatic lift and blow-down phenomenon. The stability of compliant plate seals is also limited by a variety of instabilities, including aerostatic flutter, vortex induced flutter and divergence.